This disclosure relates to compensation techniques to improve write signal controls for magnetic-medium-based storage devices, such as Hard Disk Drives (HDD), and circuitry used therein.
Hard Disk Drives (HDD) are ubiquitous in the computing environment. Existing HDD systems employ magnetic-medium-based storage devices, and the data is typically stored on circular, concentric tracks on magnetic disk surfaces. A read/write head retrieves and records data on the magnetic layer of a rotating disk as it flies on a cushion of air over the disk surface. When retrieving data, magnetic field variations are converted into an analog electrical signal, the analog signal is typically amplified, converted to a digital signal and interpreted. When writing to the track, the disk is rotated at a predetermined speed, and electrical signals applied to a magnetic read/write head floating over the track are converted to magnetic transitions on the track.
The magnetic transitions on the track represent digital data encoded so that each transition may correspond to a ONE bit value and the absence of a transition may correspond to a ZERO bit value as in a “non-return to zero” (NRZ) encoding. Multiple magnetic fields having a corresponding polarity can be transferred onto the track by the read/write head, thereby forming magnets. Magnets can be generally described as respective regions (or sectors) of the recording medium including magnetic grains having a magnetic field transferred thereto. Each magnet (i.e., each region of magnetic field variation in the recording medium) has a particular polarity, and an associated width.
In some cases, writing involves a high frequency bit, which can also cause the formed magnet to have a shorter length. The short magnet may require an additional amount of time for the magnetic field to spread out in the written track. However, in some instances, shortly after forming the short magnet, the read/write head might quickly switch the polarity applied to the recording medium in order to record the next bit. Thus, due to this quick magnetic transition, not enough time is allowed for the shorter magnet to widen in the grain of the recording medium. Accordingly, short magnets can be typically characterized as having a small width. In the case of longer magnets, the duration between transitions allows for the magnetic field to spread within the track. Consequently, longer magnets tend to have a wider width than shorter magnets. Although wider magnets can be associated with various benefits, such as a stronger read-back signal (e.g., higher signal-to-noise ratio), wider magnets have the potential drawback of interfering with the magnetic field of a neighboring track.